This application claims priority from R.O.C. Patent Application No. 091114639, filed Jul. 2, 2002, the entire disclosure of which is incorporated herein by reference.
The present invention relates to a process of forming a bottom oxide layer in a trench on a semiconductor substrate, and more specifically, to a method of forming the bottom oxide layer by introducing a silicon nitride layer and applying the isotropic etching process.
With the advance of integrated circuit technology into the ultra large scale integrated circuit (ULSI), the sizes of various devices have become increasingly small in order to manufacture the devices and the integrated circuits with high integration. However, when the scales of devices are getting smaller, it is difficult to fabricate these fine devices by applying the prior semiconductor processes. More critical and complicated processes are required to fabricate these fine devices to maintain higher yields and throughputs. Moreover, when the dimensions of integrated circuits are getting smaller, the device may not be able to meet the requirements of customers because the operating voltage, current, and the tolerant resistance thereof are also reduced. For solving these issues, power IC devices are widely applied and developed. In a typical power IC device, the gate structure is directly manufactured in the trench of the substrate, and the drain and source structures are also defined in the trench. And before fabricating the power IC device on the substrate, a bottom oxide layer is first formed on the bottom of the trench to be an insulating member. Then the subsequent processes are performed to define the gate, drain, and source structures in the trench.
In prior art, the high density plasma (HDP) deposition process is applied to form a bottom oxide layer in a trench. FIG. 1 illustrates the condition of applying the HDP process to deposit an oxide layer 12 on a substrate 10. In the depositing process, the portion of oxide layer deposited above a trench is bombarded by-high density plasma and has some small pieces fall down in the trench 14, so the portion of oxide layer formed on the bottom of the trench 14 has a large thickness. In general, when the thickness of the oxide layer formed on the sidewall of the trench is about 500 angstroms, the thickness of the bottom oxide layer will reach about 3000 angstroms. Therefore, in the subsequent wet etching process, when the oxide layer on the sidewalls is removed completely, there remains still enough thickness of the oxide layer on the bottom of the trench to serve as a bottom oxide layer.
The HDP process can be applied to form a bottom oxide layer in a trench effectively as above, but in some semiconductor fabrication industries other methods are frequently used instead of the HDP process for forming the bottom oxide layers because HDP equipments are very expensive. Especially for semiconductor foundries, it is possible to manufacture all kinds of devices such as DRAM, Flash memory, and the like, according to the requirement and designation of customers. Therefore, it may not be economically feasible for the foundries to buy HDP deposition equipments just for manufacturing power IC devices.
Some methods have been introduced to form a bottom oxide layer in a trench without HDP deposition equipments. As seen in FIG. 2, after defining a trench on the substrate 20, an oxide layer 22 is deposited on the substrate 20, and deposited on bottoms and sidewalls of the trench. Then, a photo-resist layer is formed on the oxide layer 22 and fills the trench. An ashing process is performed to remove a portion of the photo-resist to form a photo-resist filler 24 in the trench.
As shown in FIG. 3, a portion of the oxide layer 22 is then removed by applying an etching solution. In the wet etching process, the etching solution eats away the oxide layer 22 on the sidewall along the interstices between the photo-resist filler 24 and sidewall of the trench to form the bottom oxide layer 26 on the bottom of the trench. However, because the adhesion property of the photo-resist on the oxide layer is not good, some seams will occur due to film peeling. Thus, the etchant will permeate into the bottom of the trench to erode the oxide layer 22 therein. As shown in FIG. 3, after the wet etching process, the remaining bottom oxide layer 28 has a gap defect and is disabled from effective insulating in many cases.
Embodiments of the present invention are directed to a method of forming a bottom oxide layer in a trench on a semiconductor substrate. A nitride layer is used to promote adhesion property of the photo-resist formed on the nitride layer to prevent seams from forming therebetween and to keep the bottom oxide layer from erosion.
In accordance with an aspect of the present invention, a method for forming a bottom oxide layer in a trench on a substrate comprises depositing an oxide layer along the surface of sidewall and the bottom of a trench on a semiconductor substrate which has top layers, depositing a nitride layer along surface of the oxide layer, and forming a photo-resist filler in the trench. The top surface of the photo-resist filler is lower than the top surface of the substrate to expose a portion of the nitride layer uncovered by the photo-resist filler. The exposed portion of the nitride layer is removed to expose the oxide layer underneath. A portion of the oxide layer on the sidewall of the trench is removed to form a bottom oxide layer in the trench.
In some embodiments, the oxide layer comprises a TEOS material. A nitride layer has a thickness of about 100 to 500 angstroms, and about 200 angstroms in a specific example. The exposed portion of the nitride layer is removed by performing the isotropic etching process. The portion of the oxide layer on the sidewall of the trench is removed by the etching process. The etching process to remove the portion of the oxide layer may be performed with a buffer oxide etching (BOE) solution.
In accordance with another aspect of the invention, a method for forming a bottom oxide layer in a trench on a semiconductor substrate comprises etching a semiconductor substrate to form a trench thereon, performing the low pressure chemical vapor deposition to form an oxide layer on a semiconductor substrate and on the sidewall and bottom of a trench, depositing a nitride layer along the surface of the oxide layer, and forming a photo-resist filler in a trench. A portion of the nitride layer on the sidewall of a trench is not covered a photo-resist layer and is exposed. The exposed potion of the nitride layer is removed for exposing the oxide layer underneath. The oxide layer on a semiconductor substrate and on the sidewall of a trench is removed to have a remaining portion of the oxide film covered by the photo-resist filler on the bottom of a trench. The method further comprises removing the photo-resist filler, and removing the nitride layer to expose the remaining portion of the oxide layer in the trench.
In accordance with another aspect of the present invention, a method of forming a bottom oxide layer in a trench on a semiconductor substrate comprises depositing a nitride layer and an oxide layer on a semiconductor substrate in sequence, defining a trench pattern in the oxide layer and the nitride layer to expose a portion of the surface of the substrate, etching the exposed substrate to form a trench therein by applying the oxide layer and the nitride layer to serve as etching masks, forming a TEOS material layer on the oxide layer and the surface of sidewall and the bottom of a trench, forming a nitride layer on the TEOS material layer, coating a photo-resist layer on the substrate to fill the trench, performing an exposing process to cure the lower portion of the photo-resist layer in a trench, removing the upper portion of the photo-resist layer to form a photo-resist filler in a trench for exposing a portion of the second nitride layer on the top surface of the semiconductor substrate and on the sidewall of a trench, removing the exposed portion of the second nitride layer for exposing the TEOS material layer underneath, and removing the TEOS material layer on the oxide layer and the sidewall of a trench. A portion of the TEOS material layer remains on the bottom of a trench. The method further comprises removing the photo-resist filler, and removing second the nitride layer to expose the remaining portion of the TEOS material layer in a trench.